Obstacle detection apparatus for vehicles

1. An obstacle detection apparatus for vehicles, the obstacle detection apparatus mounted to a vehicle and comprising: a first probe wave sensor that is arranged at a predetermined part of a placement surface of the vehicle, and that has a detectable range to detect a direct wave distance as a distance to an obstacle by transmitting a probe wave and receiving a reflection wave of the probe wave reflected by the obstacle; a second probe wave sensor that is arranged at a position of the vehicle where the second probe wave sensor receives the reflection wave, and that has a detectable range to detect a distance to the obstacle by receiving the reflection wave; a distance difference calculator that calculates a distance difference between a direct wave distance detected by the first probe wave sensor and an indirect wave distance detected by the second probe wave sensor; a change amount calculator that calculates an amount of change in the indirect wave distance; an approach determinator that determines whether the obstacle is present in an undetectable range, which is a region between the placement surface and an overlapping region of the detectable range of the first probe wave sensor and the detectable range of the second probe wave sensor, based on a determination of whether the distance difference is smaller than or equal to a predetermined threshold value, and whether the indirect distance is decreasing based on the amount of change in the indirect wave distance; and a distance determinator that sets an obstacle distance for a driver assistance control to be less than or equal to a predetermined distance range based on the indirect wave distance being outside of the predetermined distance range, in response to the approach determinator determining that the obstacle is approaching the undetectable range in a condition that (i) the distance difference is smaller than or equal to the predetermined threshold value, and (ii) the distance difference is decreasing based on the amount of change in the indirect wave distance, wherein the direct wave distance is a distance from the first probe wave sensor to the obstacle, and is detected by the first probe wave sensor, wherein the indirect wave distance is a half of a sum of the distance from the first probe wave sensor to the obstacle and a distance from the obstacle to the second probe wave sensor, and is detected by the second probe wave sensor, and wherein the undetectable range is a range in which the indirect wave distance and the direct wave distance cannot be detected.

2. The obstacle detection apparatus for vehicles according to claim 1 , wherein the distance determinator determines the obstacle distance to be within a short distance range closer to the vehicle than the predetermined distance range based on the indirect wave distance being outside of the predetermined distance range, in a case where the approach determinator determines that the obstacle is present between the first probe wave sensor and the second probe wave sensor and the obstacle is approaching the vehicle.

3. The obstacle detection apparatus for vehicles according to claim 1 , wherein the distance determinator determines the obstacle distance to be less than or equal to the predetermined distance range based on the indirect wave distance being outside of the predetermined distance range and based on the vehicle moving, in a case where the approach determinator determines that the obstacle is present between the first probe wave sensor and the second probe wave sensor and the obstacle is approaching the vehicle.

4. The obstacle detection apparatus for vehicles according to claim 3 , further comprising: a moving/stopped state acquisition device that acquires information indicative of whether a moving/stopped state of the vehicle is a moving state or a stopped state, wherein the distance determinator determines that the vehicle is moving for a preset period of time, based on the information indicative of whether the moving/stopped state acquired by the moving/stopped state acquisition device indicates a change from the moving state to the stopped state.

5. The obstacle detection apparatus for vehicles according to claim 2 , wherein, based on the obstacle being detected in a detection area around the short distance range after the obstacle distance after determined as being within the short distance range, the distance determinator determines the obstacle distance to be a distance, which is defined based on the direct wave distance and the indirect wave distance.

6. The obstacle detection apparatus for vehicles according to claim 5 , wherein, based on the obstacle being detected in a detection area around the short distance range and based on the indirect wave distance increasing after the obstacle distance is determined as being within the short distance range, the distance determinator determines the obstacle distance to be a distance, which is defined based on the direct wave distance and the indirect wave distance.

7. The obstacle detection apparatus for vehicles according to claim 1 , wherein the approach determinator determines, based on the distance difference calculated by the distance difference calculator and the amount of change calculated by the change amount calculator, whether the obstacle is present between the first probe wave sensor and the second probe wave sensor and whether the obstacle is approaching the vehicle.

8. The obstacle detection apparatus for vehicles according to claim 7 , wherein, in a case where the distance difference is not calculated because the direct wave distance is not calculated, the approach determinator determines, based on the amount of change calculated by the change amount calculator, whether the obstacle is present between the first probe wave sensor and the second probe wave sensor and whether the obstacle is approaching the vehicle, based on the distance difference not being calculated and the indirect wave distance being calculated.

9. The obstacle detection apparatus for vehicles according to claim 1 , wherein the first probe wave sensor and the second probe wave sensor are arranged at a central part in a vehicle width direction on an end face in a front-back direction of the vehicle.

10. The obstacle detection apparatus for vehicles according to claim 1 , wherein, in response to a line parallel to an advancing direction of the vehicle and passing the first probe wave sensor being defined as a first line, and a line parallel to the advancing direction of the vehicle and passing the second probe wave sensor being defined as a second line, the approach determinator determines, based on the indirect wave distance, whether the obstacle is present between the first line and the second line and whether the obstacle is approaching the vehicle.

11. The obstacle detection apparatus for vehicles according to claim 2 , wherein the short distance range includes an undetectable range where the obstacle is undetectable.

12. An obstacle detection apparatus for vehicles, the obstacle detection apparatus mounted to a vehicle and comprising: a first probe wave sensor configured to detect a direct wave distance to an obstacle by transmitting a probe wave and receiving a reflection wave of the probe wave that is reflected by the obstacle; a second probe wave sensor configured to receive the reflection wave and detect a distance to the obstacle by receiving the reflection wave; a distance difference calculator that calculates a distance difference between a direct wave distance detected by the first probe wave sensor and an indirect wave distance detected by the second probe wave sensor; a change amount calculator that calculates an amount of change in the indirect wave distance; an approach determiner that determines whether the obstacle is approaching an undetectable range based on a determination of whether the direct wave distance is detected, whether the distance difference is smaller than or equal to a predetermined threshold value, the undetectable range comprising a gap within which the direct wave distance and the indirect wave distance cannot be detected, the gap defined by the vehicle and obstacle detection ranges of the first probe wave sensor and the second probe wave sensor, and whether the indirect distance is decreasing based on the amount of change in the indirect wave distance; and a distance determiner that sets an obstacle distance for a driver assistance control to be less than or equal to a predetermined distance range in response to the approach determiner determining that the obstacle is approaching the undetectable range in a condition that (i) the distance difference is smaller than or equal to the predetermined threshold value, and (ii) the distance difference is decreasing based on the amount of change in the indirect wave distance, and (iii) despite the indirect wave distance to the obstacle being determined to be greater than the predetermined distance range, wherein the direct wave distance is a distance from the first probe wave sensor to the obstacle, and is detected by the first probe wave sensor, and wherein the indirect wave distance is a half of a sum of the distance from the first probe wave sensor to the obstacle and a distance from the obstacle to the second probe wave sensor, and is detected by the second probe wave sensor.